1. NETE 0510 Presented by Dr.Apichan Kanjanavapastit
Multiplexing
NETE 0510
Presented by
Dr.Apichan Kanjanavapastit

2. What is Multiplexing
Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link
Today’s technology includes high-bandwidth media such as optical fiber, each of these has a carrying capacity far in excess of that needed for the average transmission signal
An efficient system maximizes the utilization of all facilities

3. Many to One/One to Many
In a multiplexed system, n devices share the capacity of one link
The stream of traffic from each device is sent to a multiplexer (MUX), which combines them into a single stream (many to one)
At the receiving end, that stream is fed into a demultiplexer (DEMUX), which separates the stream back into its component transmissions (one to many) and directs them to their intended receiving devices

4. Categories of Multiplexing
Signals are multiplexed using 3 basic techniques: frequency-division multiplexing (FDM), time-division multiplexing (TDM), and wave-division multiplexing (WDM)
TDM is further subdivided into synchronous TDM (usually just called TDM) and asynchronous TDM, also called statistical TDM or concentrator

5. Frequency-Division Multiplexing (FDM)
FDM is an analog technique
In FDM, signals generated by each sending device modulate different carrier frequencies
Carrier frequencies are separated by enough bandwidth to accommodate the modulated signal

6. The FDM Process: Multiplexing

7. The FDM Process: Demultiplexing

8. Amplitude Modulation Techniques for Analog Signals
Amplitude Modulation (AM)
Double-sideband suppressed carrier (DSB-SC) modulation
Single-sideband suppressed carrier (SSB) modulation

9. Amplitude Modulation (AM)
modulator
4 kHz
6 kHz
10 kHz
14 kHz
10 kHz

10. Double-sideband suppressed carrier modulation (DSB-SC)
modulator
4 kHz
6 kHz
10 kHz
14 kHz
10 kHz

11. Single-sideband suppressed carrier (SSB)
DSB-SC
modulator
Band Pass
Filter
6 kHz
10 kHz
14 kHz
6 kHz
10 kHz
4 kHz
SSB
10 kHz

12. Example#1
Five channels, each with a 100-kHz bandwidth, are to be multiplexed together. What is the minimum bandwidth of the link if there is a need for a guard band of 10 kHz between the channels to prevent interference?

13. Example#2
Four digital signals, each transmitting at data rate of 1 Mbps, use a satellite channel of 1 MHz. Design an appropriate configuration, using FDM.

14. ITU-T Multiplexing Plan for Analog Telephone System

15. ITU-T Multiplexing Plan for Analog Telephone System (cont.)
Incoming Ch.
BPF
kHz 1
108 kHz
BPF
Multiplex signal
kHz 2
104 kHz
BPF
kHz 12
64 kHz 12 11 10 9 8 7 6 5 4 3 2 1 60 64 68 72 76 80 84 88 92 96
100
104
108

16. Supergroup multiplexer Mastergroup multiplexer
12 voice frequency
Channel input (0-4 kHz)
Supergroup output
60VF. 240 kHz bandwidth
F=108
108
F=3396
3048
2844
F=104
104
Group output
12 VF. 48 kHz bandwidth
F=3148
2836
Mastergroup
output
600VF.
2.52 MHz
bandwidth
2569
F=100
100
F=2900
2588
F=96 96
2348
F=612
552
F=2652
2340
F=92 92
F=564
504
2100
F=2356
F=88 88
2044
F=516
456
1804
F=84 84
F=2108
1796
F=468
408
1556
F=80 80
F=1860
F=420
360
1548 76
1308
F=76
312
F=1612
1300
5 Group inputs
F=72
1060 72
10 Supergroup inputs
F=1364
1052
F=68 68
812
Supergroup multiplexer
F=1116
F=64
804 64
564 60
Group multiplexer
Mastergroup multiplexer

17. Application Example of FDM: Cable TV
Coaxial cable has a bandwidth up to several hundreds megahertz
The bandwidth of the coaxial cable is normally divided into 6 MHz using FDM
Each band provides a TV channel or data transmission

18. Wave-Division Multiplexing (WDM)
WDM is conceptually the same as FDM, except that the multiplexing and demultiplexing involve light signals transmitted through fiber optic channels
Combining and splitting of light sources are easily handled by a prism

19. Recall Attenuation in Optical Fiber
0.5
1.0
1.5
2.0
2.5
3.0
First
Window
Second
Window
Third
Window
ATTENUATION (dB/km)
800
900
1000
1100
1200
1300
1400
1500
1600
1700
WAVELENGTH (nm)
850nm
1310nm
1550nm

20. Time-Division Multiplexing (TDM)
TDM is a digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving ends
TDM can be implemented in 2 ways: TDM and asynchronous TDM

21. Synchronous TDM
In synchronous TDM, the term synchronous has a different meaning from synchronous transmission
Hear synchronous means that the multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit
Time slots are grouped into frames. A frame consists of one complete cycle of time slots

22. Interleaving in Synchronous TDM
Synchronous TDM can be compared to a very fast rotating switch
As the switch opens in front of a device, that device has the opportunity to send a specified amount of data into the path
The switch moves from device to device at a constant rate and in a fixed order. This process is called interleaving which can be done by bit, by byte, or by any other data unit

23. Interleaving in Synchronous TDM (cont.)

24. Example#3
The data rate for each input connection is 1 kbps. If 1 bit at a time is multiplexed (a unit is 1 bit), what is the duration of (a) each input slot, (b) each output slot, and (c) each frame?

25. Example#4
The figure below shows synchronous TDM with a data stream for each input and one data stream for the output. The unit of data is 1 bit. Find (a) the input bit duration, (b) the output bit duration, (c) the output bit rate, and (d) the output frame rate.

26. Example#5
Four channels are multiplexed using TDM. If each channel sends 100 bytes /s and we multiplex 1 byte per channel, show the frame traveling on the link, the size of the frame, the duration of a frame, the frame rate, and the bit rate for the link.

27. Example#6
A multiplexer combines four 100-kbps channels using a time slot of 2 bits. Show the output with four arbitrary inputs. What is the frame rate? What is the frame duration? What is the bit rate? What is the bit duration?

28. Multiple Slots Multiplexing

29. Example#7
Two channels, one with a bit rate of 100 kbps and another with a bit rate of 200 kbps, are to be multiplexed. How this can be achieved? What is the frame rate? What is the frame duration? What is the bit rate of the link?

30. Framing Bits in Synchronous TDM
Because the time slot order in a synchronous TDM system does not vary from frame to frame, very little overhead information needs to be included in each frame
However, various factors can cause timing inconsistencies. For this reason, one or more synchronization bits are usually added to the beginning of each frame

31. Framing Bits in Synchronous TDM (cont.)
These bits, called framing bits, that allows the demultiplexer to synchronize with the incoming stream so that it can separate the time slot accurately
In most cases, this synchronization information consists of one bit per frame, alternating between 0 and 1

32. Example of a Data Rate Calculation in Synchronous TDM
There are 4 input sources on a synchronous TDM link, where transmissions are interleaved by character
If each source is creating 250 characters per second, and each frame is carrying 1 character from each source, the transmission path must be able to carry 250 frames per second
Assuming that each frame is 33 bits long: 32 bits for the 4 characters plus 1 framing bit; the data rate of the multiplexed line will be 8250 bps (250 frames with 33 bits per frame)

33. Bit Stuffing in Synchronous TDM
Recall that the time-slot length is fixed and it is possible to connect devices of different data rate to a synchronous TDM
For this technique to work, the different data rates must be integer multiples of each other
When the speeds are not integer multiple of each other, they can be made to behave as if they were, by a technique called bit stuffing

34. Bit Stuffing in Synchronous TDM (cont.)
The multiplexer adds extra bits to a device’s source stream to force the speed relationships among the various devices into integer multiples of each other
The extra bit are then discarded by the demultiplexer

35. Asynchronous TDM
In synchronous TDM, since the time slots are preassigned and fixed, whenever a connected device is not transmitting, the corresponding slot is empty and that much of the path is wasted
Asynchronous TDM or statistical TDM is designed to avoid this type of waste
In this context, asynchronous means flexible or not fixed
The number of time slots in asynchronous TDM frame is based on a statistical analysis of the number of input lines that are likely to be transmitting at any given time

36. Asynchronous TDM (cont.)
Like synchronous TDM, asynchronous TDM allows a number of lower-speed input lines to be multiplexed to a single higher-speed line
Unlike synchronous TDM, the total speed of the input lines can be greater than the capacity of the path
In asynchronous TDM, the frame can contain a lower number of time slots when compared with synchronous TDM

37. Example of Asynchronous TDM Frames

38. Addressing and Overhead in Asynchronous TDM
In the absence of fixed positional relationships, each time slot must carry an address telling the demultiplexer how to direct the data.